Single aperture multiple beam antennas



J. H. HARRIS July 1, 1969 SINGLE APERTURE MULTIPLE BEAM ANTENNAS FiledOct. 6, 1966 United States Patent 3 453 632 SINGLE APERTURE MULTIPLEBEAM ANTENNAS Jay Howard Harris, Bellevue, Wash., assignor to the UnitedStates of America as represented by the Secretary of the Air Force FiledOct. 6, 1966, Ser. No. 585,228 Int. Cl. H01q 13/02 US. Cl. 343-772 6Claims This invention relates generally to multiple channel antennasand, more particularly, to multiple channel antennas which are capableof radiating a plurality of beams of microwave energy from a singleaperture. Additionally, the beams from the antenna may be at widelydifferent frequencies wherein the beams are arbitrarily oriented inspace.

Generally, multiple beam antennas require extensive structures which,for aircraft purposes, increases the weight. In addition, a plurality ofapertures which are not capable of flush mounting to an aircraft orspace vehicle cause added expense and structural modification to allowfor this installation.

Accordingly, it is a primary object of this invention to providemultiple channel antennas capable of radiating two or more beams ofmicrowave energy from a single aperture.

It is another object of this invention to provide multiple channelantennas for a plurality of beams which are identically polarized.

It is still another object of this invention to provide antennas havinga plurality of channels which radiate from a single aperture.

It is a further object of this invention to provide multiple channelantennas wherein the beam for each channel originates from anindependent feed.

It is a still further object of this invention to provide a multiplechannel antenna capable of radiating a plurality of beams of more thanone microwave frequency.

Another object of this invention is to provide a multiple channelantenna having beams at widely different frequencies which arearbitrarily oriented in space.

Still another object of this invention involves the production ofmultiple channel antennas which do not employ lenses or reflectors ordirectional couplers to produce multiple beams. Further, when a singlefrequency is used, the antenna is still capable of providing multiplebeams.

A further object of this invention involves a multiple channel antennaof multiple frequencies which does not employ either optical or multiplemode wave guide techniques or spatial orientation in the aperture plane.

A still further object of this invention involves the production ofmultiple channel antennas which are economical to fabricate ofconventional, currently available materials that lend themselves to massproduction manufacturing techniques.

These and other advantages, features and objects of the invention willbecome more apparent from the following description taken in connectionwith the illustrative, embodiments in the accompanying drawings,wherein:

FIGURE 1 is a schematic representation of a multiple channel antennacapable of radiating two or more narrow, identical polarized beams of amicrowave energy from a single aperture;

FIGURE 2 is a representation of the leaky wire grid wall details of theembodiments of FIGURE 1; and

FIGURE 3 is a representation of a multiple frequency, multiple channelantenna utilizing leaky wire grid walls.

The antenna techniques of this invention provide for leaky wavepropagation in each channel with a phase velocity that is determined bythe width of the channel and the properties of the walls. When the waveloses power at a regular rate, radiation into space to form beams plus acoupling into leaky waves of other channels is eifected. When the ratioof power radiated into space to that coupled into the other channels ishigh, a multiple beam antenna with port isolation is obtained. The wavesare stated to be of the leaky type because some portion of the instantenergy is transmitted through the wall at each reflection.

It has been found that leaky waves are essentially radial wave guidemodes and when leaky wire grids and free space layers are alternated,the volume bounded by the leaky grids may be employed as propagationchannels to produce a multiple beam antenna that radiates from a singleaperture. The antenna may be thought of as being the equivalent tohaving one antenna in front of another. The obtaining of leaky wavesrequire a layer of permeability less than that of free space, which inthese embodiments is provided by walls comprised of regular arrays ofwires.

Referring to FIGURE 1 there is shown a multiple channel antenna havingupper and lower opposed, generally parallel, rectangular, metallic,conducting planes 10 and 12 which are interconnected by means of ametallic, conducting, rear side wall 14 extending along opposed edges ofthe planes 10 and 12. Leaky wire grid walls 16 define separatepropagation channels, the wall details of which are illustrated mostclearly in FIGURE 2. Each leaky wire grid wall 16 is comprised of atleast two parallel layers or rows of wires 18 which make electricalcontact with both of the metallic, conducting planes 10 and 12.

A plurality of rows of wires are utilized in order to provide thicknessto the walls 16, since, when the walls of the channel are thick, welldefined leaky waves may be propagated; however, the attenuation rate ofthe waves must also be considered into the selection of the wallthickness. If the thickness is too great, the rate of power loss may beinsuflicient for practical applications. It has been experimentallyverified that a spacing of .25 inch to .3 inch between the rows of wires18 produced the required waves. The spacing between adjacent wires in arow is determined by the frequency of the energy in the channels.

Thus, a planar array is formed from stacked linear arrays and multiplebeams are produced in the plane that is parallel to the linear arrays.Microwave energy is introduced into one or more of the channels whichform linear arrays in the region between the leaky wire grid walls 16 ofFIGURE 1 in order to have energy propagate as a TE leaky wave mode withthe propagation constant controlled by the width of the channel and theproperties of the walls 16. Power is radiated by the leaky wave mode andforms a beam in space from each channel which is directly related to thepropagation constant of the leaky wave mode. The critical angle of aleaky wire grid wall 16 is selected so that it lies between the beampointing angle of the channel below the wall and the beam pointing angleof the channel above the wall. The width of each channel is selectedsuch that succeeding channels which are closer to the aperture on theside opposite the rear side wall 14 generate beams which are closer toend-fire.

An antenna, as described relative to FIGURE 1, with only two channelscould be employed as a Doppler velocity sensor radar antenna since fourbeams with the same polarization may be generated and the velocityinformation may be obtained by measurement of the frequency shift ofeach beam.

The antenna of FIGURE 3 is capable of radiating a plurality of beams atwidely different frequencies with arbitrary orientations in space. Thisantenna is comprised of metallic, conducting planes 10' and 12' with ametallic, conducting, rear side wall 14 connected as described rela- 3tive to FIGURE 1. In this embodiment, leaky wire grid walls 16 are alsoprovided; however, metallic conducting walls 20 are added parallel tothe metallic, conducting, planes and 12' thus defining a series of K,,band channels 22 with a pair of X-band channels 24 adjacent thereto.Finally, an S-band channel 26 is provided. Each channel in thisembodiment would be fed its energy from appropriately tapered waveguides.

Thus, beams may be produced at more than one frequency with each beamgenerated by the same wave guide mode. All of this is done with a singleaperture opposite the rear side wall 14 wherein the sensitivity of theantenna to fabrication errors is small. The propagation channels of thisembodiment are bounded above and below the conducting planes and on thesides by the leaky wire grid walls except for the rear side wall. A TEleaky wave mode at appropriate frequency is launched in each channel byan appropriate, tapered wave guide (not shown). The height of eachchannel is selected for design convenience while the width is dictatedby the propagation constant to yield the beam in a desired direction.The walls 16 are designed to appear effectively impermeable tofrequencies propagating to the left While they are semi permeable to thechannel to the left and invisible to frequencies propagated in channelsfurther to the left. This design is obtained if the equivalent frequencyof a wall is taken equal to the frequency of the channel to the left ofthe wall; therefore, closer spacings of the wires 18' forming the leakywire grid walls 16 are used for the higher frequencies.

By having a frequency channel antenna of the type described relative toFIGURE 3, communication may be effected on one beam while ground mappingmay be accommodated on another with the same aperture.

Although the invention has been described relative to particularembodiments, it should be understood that the invention is capable of avariety of alternative embodiments within the spirit and scope of theappended claims. For example, the channels may be formed by insertingpolyfoam spacers between the leaky grid walls 16, which may beconstructed of narrow strips of very thin, etched circuit boards. Thewires may be etched on one side of the strip and a conducting materialon the edges of the strip would insure electrical contact between thewires 18' and the conducting planes 10, 12 or 10', 12. A single wall isformed by more than one row of wires, thus at least a pair of the stripswould be utilized for each wall. In addition, conventional microwaveenergy absorbent material may be provided at the end of the channelsremote from the feed in order to avoid the unwanted radiation of energytherefrom.

I claim:

1. Means for radiating a plurality of polarized beams of microwaveenergy from a single aperture comprising:

a plurality of channels, each forming a linear array, said channelsbeing formed by a pair of opposed, generally parallel, metallic,conducting planes,

a rear side wall extending along an edge of each of said opposedconducting planes, and

leaky wire grid walls in electrical contact with and extending betweensaid opposed conducting planes and parallel to said rear side wall.

2. Means as defined in claim 1 wherein said leaky wire grid walls areformed of at least two parallel rows of wires which make contact withsaid opposed conducting walls.

3. Means as defined in claim 2 wherein the wires of said rows of wiresforming said leaky wire grid walls are equally spaced.

4. Means as defined in claim 2 wherein said wires of said rows of Wiresforming said leaky wire grid walls are equally spaced in each row butthe wires in some of said walls do not have the same spacing as inothers of said walls.

5. Means as defined in claim 4 wherein the aperture from which saidantenna radiates is opposite said rear side and the channels arearranged such that the channels having higher frequencies and closerspacing of the wires in said wall are remote from said aperture.

6. Means as defined in claim 4 including additional metallic, conductingplanes between and parallel with said pair of opposed, generallyparallel, metallic, conducting planes, said additional metallic,conducting planes being in contact with said rear side wall.

References Cited UNITED STATES PATENTS 2,957,173 10/1960 Rotman 3437723,015,100 12/1961 Rotman 343772 ELI LIEBERMAN, Primary Examiner.

U.S.Cl.X.R.

1. MEANS FOR RADIATING A PLURALITY OF POLARIZED BEAMS OF MICROWAVEENERGY FROM A SINGLE APERTURE COMPRISING: A PLURALITY OF CHANNELS, EACHFORMING A LINEAR ARRAY, SAID CHANNELS BEING FORMED BY A PAIR OF OPPOSED,GENERALLY PARALLEL, METALLIC, CONDUCTING PLANES, A REAR SIDE WALLEXTENDING ALONG AN EDGE OF EACH OF SAID OPPOSED CONDUCTING PLANES, ANDLEAKY WIRE GRIDE WALLS IN ELECTRICAL CONTACT WITH AND EXTENDING BETWEENSAID OPPOSED CONDUCTING PLANES AND PARALLEL TO SAID REAR WALL.